Authentication of packaged products

ABSTRACT

Methods are provided for producing an authenticated packaged product. A digital signature, dependent on unique message data for the product, is generated via a digital signature scheme using a secret signing key. The message data is provided on at least one of the product and packaging. The digital signature is provided on the other of the product and packaging, and the product is packed in the packaging. The digital signature can be generated via a fuzzy-message digital signature scheme having a verification algorithm for verifying the digital signature in relation to fuzzy data within a predetermined difference measure of the message data. Methods and systems for authenticating such packaged products are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/440,816 filed Feb. 23, 2017, the complete disclosure of which isexpressly incorporated herein by reference in its entirety for allpurposes.

BACKGROUND

The present invention relates generally to authentication of packagedproducts.

Currently, authentication of packaged products relies on printedinformation such as text, logos etc., on the packaging and/or product.It is easy to change or reproduce such information in order tomisrepresent a product in some way, e.g. to present a fake orcounterfeit product as genuine, and it is difficult for users toidentify fraudulent products. As a particularly pertinent example, thehealth care industry has been a frequent target for fraud of thisnature. Circulation of unauthorized or counterfeit medical products iswidespread and has significant health implications. For example, medicaltest devices such as HIV (human immunodeficiency virus), malaria,hepatitis and pregnancy tests are commonly counterfeited. Techniquesinclude imitating genuine product packaging for counterfeit products,altering critical product information, such as expiry dates, onpackaging, and substituting products from one authentic packaging intoanother, such as the placement of pregnancy tests into packaging for HIVtests. The World Health Organization considers that counterfeiting ofsuch tests compromises the detection and eradication of some diseases.

SUMMARY

According to at least one embodiment of the present invention there isprovided a method for producing an authenticated packaged product. Themethod comprises: generating a digital signature, dependent on uniquemessage data for the product, via a digital signature scheme using asecret signing key; providing the message data on at least one of theproduct and packaging; providing the digital signature on the other ofthe product and packaging; and packing the product in the packaging.

Methods embodying the invention uniquely bind a product to its packagingvia the digital signature scheme. The digital signature can beauthenticated for the message data using a verification algorithm of thesignature scheme. Such verification algorithms use a verification keywhich corresponds to the secret signing key used to generate thesignature. A forger cannot generate a valid signature without knowledgeof the secret signing key, and cannot misrepresent fraudulent products,e.g. by replacing products in genuine packaging. Methods embodying theinvention thus provide for secure authentication of packaged products.

In preferred embodiments, the digital signature is generated via afuzzy-message digital signature scheme having a verification algorithmfor verifying the digital signature in relation to fuzzy data within apredetermined difference measure of said message data. Cryptographicconstructions for generation and verification of signatures infuzzy-message signature schemes are presented below. Such afuzzy-message digital signature scheme permits verification of a digitalsignature even if the message data suffers some corruption so thatmessage data used on verification is different, up to a predefinedlimited extent, from that used to generate the signature. This is ahighly advantageous feature in that it accommodates some limited degreeof error, which may be necessary due to constraints inherent inimplementations of the scheme, while still permitting detection ofcounterfeits. The message data may be incorrectly presented for variousreasons, e.g. due to space constraints on the product/packaging and/ortolerances in mechanisms for representing messages resulting in errorson readback. In embodiments based on medical test devices, for example,space for messages may be very limited, and mechanisms for presentingthe message data may have inherent inaccuracies as will be illustratedby examples below.

In general, the message data may be provided on only one of the productand packaging, in which case the signature is provided on the other, orthe message data may comprise data on both of the product and packaging,in which case the signature may be provided on either. Where the productis a medical test device, the message data preferably comprises (atleast) a first message which is provided on the test device, and thedigital signature is most conveniently provided on the packaging. Wherethe medical test device is operable by application of a fluid to thedevice, the first message may be provided on the device in a form atleast part of which is only revealed on application of the fluid to thedevice. The first message is thus hidden until the test is used, furtherinhibiting malicious intervention.

At least one further embodiment of the invention provides a method forauthenticating a packaged product having unique message data for theproduct on at least one of the product and packaging and a digitalsignature, dependent on the message data, on the other of the productand packaging, the digital signature being generated via a digitalsignature scheme using a secret signing key. The method includes, at averifier computer having a reader device operatively associatedtherewith, reading, via the reader device, the digital signature and themessage data on the product and packaging. The method further comprisesusing a verification key corresponding to the secret signing key toverify the digital signature in relation to the read message data. Inpreferred embodiments where the digital signature is generated via afuzzy-message digital signature scheme, the method includes verifyingthe digital signature in relation to read message data within apredetermined difference measure of the message data provided on theproduct and/or packaging.

In a first construction of a fuzzy-message digital signature scheme, themessage data comprises a first message m₁ provided on the opposite oneof the product and packaging to the digital signature, and the digitalsignature comprises the first message m₁ and signature data Σ generatedby signing signature-input data, comprising the first message m₁, usingthe secret signing key. With this construction, the packaged product canbe authenticated by verifying the signature data Σ in relation to thefirst message m₁ in the digital signature using the verification key,and determining if the read message data is within the predetermineddifference measure of the first message m₁ in the digital signature.Only if the signature data Σ is so verified, and the read message datais within the predetermined difference measure, will the digitalsignature be deemed valid (and validity may be subject to additionalcriteria discussed below).

In a second, preferred construction of a fuzzy-message digital signaturescheme, the message data comprises a first message m₁ provided on theopposite one of the product and packaging to the digital signature, andthe digital signature includes signature data Σ generated by encodingthe first message m₁ to produce an encoded message e(m₁) which comprisesthe first message m₁ and parity data p, and signing signature-inputdata, comprising the first message m₁, using the secret signing key. Thedigital signature then also includes the parity data p. With thisconstruction, the packaged product can be authenticated by decoding theread message data using the parity data p to obtain a decoded message,and verifying the signature data Σ in relation to the decoded messageusing the verification key. Only if the signature data Σ is so verifiedwill the digital signature be deemed valid. (Again, additional validitycriteria may be applied here). With this construction, the first messagem₁ is not revealed by the digital signature, while still permittingverification via the fuzzy-message signature scheme.

Both constructions described above can be adapted to accommodate messagedata which includes a second message m₂ on the same one of the productand packaging as the signature. In these embodiments, the first messagem₁ may provide the fuzzy data in which some error is permitted in theverification process of the signature scheme, and the second message m₂may be a “rigid” message, for which no error (fuzziness) is permitted onverification. This offers further advantages discussed below.

Preferred authentication methods may include, at the verifier computer,sending the read message data and digital signature via a network to asignature-management server for checking, at the server, whether thatdigital signature has been previously sent to the server, and inresponse to receipt from the server of a notification that the digitalsignature had been previously sent to the server, determining that thedigital signature is invalid in relation to the read message data. Thisoffers additional protection against any possible reproduction of themessage data and signature from a genuine packaged product on acounterfeit. At least one further embodiment of the invention provides asystem comprising a verifier computer as described above and a signaturemanagement server operable for communication via a network. Thesignature management server is adapted, in response to receipt of theread message data and digital signature from the verifier computer, tocheck whether that digital signature has been previously received andstored in storage operatively associated with the server, if so to sendthe verifier computer a first notification indicating that the signatureis invalid and, if not, to use the verification key to verify thedigital signature in relation to the read message data and, onverification of the digital signature, to send the verifier computer asecond notification indicating that the signature is valid and to storethe signature in said storage. The verifier computer is further adaptedto determine that the digital signature is invalid in response toreceipt of the first notification, and to determine that the digitalsignature is valid in response to receipt of the second notification.The signature verification step at the server offers additionalprotection against the possibility of abusive reporting of signaturesfrom genuine packaged products in an attempt to undermine the system.

Further embodiments of the invention provide packaged products producedby a method described above, and computer program products for causing averifier computer to perform an authentication method described above.

Embodiments of the invention will be described in more detail below, byway of illustrative and non-limiting example, with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 indicates step of an authenticated packaged-product productionmethod embodying the invention;

FIG. 2 is a schematic representation of an authentication systemembodying the invention;

FIG. 3 is a generalized schematic of a computer in the FIG. 2 system;

FIG. 4 is a schematic representation of a medical test device embodyingthe invention;

FIGS. 5 and 6 illustrate mechanisms for representing message data onmedical test devices embodying the invention;

FIG. 7 indicates steps performed in the FIG. 2 system in operation of afirst authentication method embodying the invention; and

FIG. 8 indicates steps performed in the FIG. 2 system in operation of asecond authentication method embodying the invention.

DETAILED DESCRIPTION

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

FIG. 1 indicates basic steps of a process for producing an authenticatedpackaged product embodying the invention. Steps of this process may beperformed by a product manufacturer during manufacture of theproduct/packaging and/or as part of the packing process. Particularsteps may be performed by a (general- or special-purpose) computer ofthe manufacturer as part of an automated production process. In step 1,the manufacturer computer selects unique message data m for a currentproduct. In the preferred embodiments to be described, the message datam comprises a first message m₁ and a second message m₂. The firstmessage m₁ comprises data which is unique to the product, e.g. a productserial number or other identifier unique to the product. The secondmessage m₂ may comprise more general data, such as data indicatingproduct type, manufacturer details, expiration date, etc. as appropriatefor the product, and may not be unique to a particular product. In step2, the manufacturer computer generates a digital signature, denoted byσ, dependent on the message data m. The signature σ is generated via adigital signature scheme, described below, using a secret signing key skof the manufacturer. The key sk is the secret key of a cryptographicsigning/verification key-pair (pk,sk) where the verification key pk is apublic key which can be certified by a trusted CA (CertificationAuthority) in accordance with a standard PKI (Public KeyInfrastructure). In step 3 of the process, the first message m₁ isprovided on the product. The message m₁ may be applied to the product invarious ways, and at various stages of the overall manufacturingprocess, depending on the nature of the product and the particularmechanism for representing the message m₁ on the product. For example,the message m₁ may be provided on the product during production of theproduct itself, or may be applied to the product after production. Instep 4, the digital signature σ and the second message m₂ are providedon the packaging for the product. Again, the signature σ and message m₂may be applied to the packaging during or after production asappropriate. In step 5, the product is packed in the packaging, and theprocess is complete.

The basic steps described above may be performed in any convenient orderdepending on the particular nature of the product, packaging and packingprocess and the way in which data is represented on theproduct/packaging. The data can be represented in various ways, and themanner of representation may differ for the two messages m₁ and m₂, andfor the digital signature σ. For example, data can be presented by oneor a combination of text, numerals, symbols, ink-printed dots (which maybe multi-colored), optical devices such as holograms, RFID (radiofrequency identification) tags, code patterns such as barcodes, QR(Quick Response) codes, or any other code formation or datarepresentation mechanism. Particular examples will be described furtherbelow. Moreover, the data representation mechanism may be such thatmessage data is wholly or partially hidden on the product and/orpackaging, and only revealed by later action, e.g. action taken when theproduct is used. This will be illustrated by examples below.

While the message data m comprises data m₁ and m₂ on the product andpackaging respectively above, in other embodiments message data m may beprovided on only one of the product and packaging. In such embodiments,the digital signature σ is provided on the other of the product andpackaging. Where message data m₁, m₂ is provided on both of the productand packaging, the digital signature σ may be provided on the product inalternative embodiments.

The above process provides a packaged product in which the product isuniquely and authentically bound to its packaging via the digitalsignature scheme. The digital signature σ can be authenticated for themessage data m, using the (public) verification key pk, via averification algorithm of the signature scheme. This assures that thesignature σ is valid for the message data m via the security propertiesof the signature scheme. A user can thus be assured that neither thesignature nor message data have been tampered with, and that thepackaging is genuine for the product. Signatures cannot be forged by acounterfeiter since only the product manufacturer, who knows the secretsigning key sk, can generate valid signatures, and products cannot befraudulently repackaged in genuine packaging of other products.

FIG. 2 is schematic block diagram of an authentication system forauthenticating packaged products in preferred embodiments. The system 10comprises a verifier computer 11 and a signature management server 12which are operable for communication via a network 13. (Signaturemanagement server 12 may communicate with multiple verifier computers inoperation, but the authentication procedure can be understood from thefollowing description in relation to verifier computer 11). A high-levelabstraction of functional components of verifier computer 11 and server12 is shown in the figure. Server 12 is indicated here as comprising acommunications interface (UF) 14 for communicating with verifiercomputer 11 over network 13, signature management logic 15 providingfunctionality for implementing steps of the authentication proceduredescribed below, and memory 16 for storing data used by logic 15 inoperation. This data includes the verification key pk corresponding tothe signing key sk described above, as well as any other data requiredfor operation of the protocols to be described. In operation of theauthentication scheme, server 12 also stores a signature set (denoted by{σ}) in storage, represented here by database 17, operatively associatedthe server.

Verifier computer 11 comprises a communications interface 18 forcommunications with server 12 via network 13, verifier logic 19providing functionality for implementing steps of the authenticationprocedure to be described, and memory 20 for storing data used byverifier logic 19 in operation. Again, this data includes theverification key pk and any other data required for operation of theprotocols detailed below. Verifier computer 11 has a user OF 21comprising a display for interaction with a user. The verifier computeralso has reader device 22 operatively associated therewith. Readerdevice 22 is adapted for reading data from a product 23 and packaging 24of a packaged product produced by the method of FIG. 1. In particular,reader device 22 is operable for reading a product message 25(comprising m₁) from the product 23, and also a pack message 26(comprising m₂) and a signature message 27 (comprising the digitalsignature σ) from the packaging 24.

Verifier computer 11 may be implemented by a general or special-purposecomputer which is operated by a party wishing to authenticate theproduct 23. For example, verifier computer may be implemented by ageneral-purpose user computer such as a desktop computer, laptopcomputer, tablet, notebook, palmtop, mobile phone, PDA (personal digitalassistant), or other user computer device. Alternatively, verifiercomputer 11 may be implemented by a dedicated hand-held unit in somescenarios. Reader device 22 may be integrated with verifier computer 11(e.g. an integrated camera of a mobile phone or tablet computer) or maybe coupled to verifier computer 11 (via a wired or wireless link) in anyconvenient manner. Various implementations of reader device 22 can beenvisaged according to the particular manner in which the data m₁, m₂, σis represented in messages 25, 26, 27 on the packaged product. Forexample, reader device 22 may comprise one (or a combination of) acamera, scanner, magnetic strip reader, RFID tag reader, or other sensoradapted to capture an image, scan, sense or otherwise “read” themessages 25, 26 and 27 so that data presented thereby is provided toverifier computer 11. The reader device 22 and/or verifier logic 19 mayinclude functionality for interpreting messages 25 to 27, e.g. imagesthereof captured by a camera, to extract the data according to theparticular manner of representation.

Network 13 may in general comprise one or more component networks and/orinternetworks, including the Internet. Signature management server 12may be implemented by a general- or special-purpose computer, comprisingone or more (real or virtual) machines, providing functionality forimplementing the operations described. In general, each of thefunctional blocks of devices shown in FIG. 2 may be implemented by oneor more functional components which may be provided by one or morecomputers. The logic 15 and 19 of these devices may be implemented byhardware or software or a combination thereof. The logic may bedescribed in the general context of computer system-executableinstructions, such as program modules, executed by a computingapparatus. Generally, program modules may include routines, programs,objects, components, logic, data structures, and so on that performparticular tasks or implement particular abstract data types. Thecomputing apparatus may be practiced in distributed cloud computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed cloudcomputing environment, data and program modules may be located in bothlocal and remote computer system storage media including memory storagedevices.

FIG. 3 is a block diagram of exemplary computing apparatus forimplementing a computer of the above system. The computing apparatus isshown in the form of a general-purpose computer 30. The components ofcomputer 30 may include processing apparatus such as one or moreprocessors represented by processing unit 31, a system memory 32, and abus 33 that couples various system components including system memory 32to processing unit 31.

Bus 33 represents one or more of any of several types of bus structures,including a memory bus or memory controller, a peripheral bus, anaccelerated graphics port, and a processor or local bus using any of avariety of bus architectures. By way of example, and not limitation,such architectures include Industry Standard Architecture (ISA) bus,Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, VideoElectronics Standards Association (VESA) local bus, and PeripheralComponent Interconnect (PCI) bus.

Computer 30 typically includes a variety of computer readable media.Such media may be any available media that is accessible by computer 30including volatile and non-volatile media, and removable andnon-removable media. For example, system memory 32 can include computerreadable media in the form of volatile memory, such as random accessmemory (RAM) 34 and/or cache memory 35. Computer 30 may further includeother removable/non-removable, volatile/non-volatile computer systemstorage media. By way of example only, storage system 36 can be providedfor reading from and writing to a non-removable, non-volatile magneticmedium (commonly called a “hard drive”). Although not shown, a magneticdisk drive for reading from and writing to a removable, non-volatilemagnetic disk (e.g., a “floppy disk”), and an optical disk drive forreading from or writing to a removable, non-volatile optical disk suchas a CD-ROM, DVD-ROM or other optical media can also be provided. Insuch instances, each can be connected to bus 33 by one or more datamedia interfaces.

Memory 32 may include at least one program product having one or moreprogram modules that are configured to carry out functions ofembodiments of the invention. By way of example, program/utility 37,having a set (at least one) of program modules 38, may be stored inmemory 32, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystem, one or more application programs, other program modules, andprogram data, or some combination thereof, may include an implementationof a networking environment. Program modules 38 generally carry out thefunctions and/or methodologies of embodiments of the invention asdescribed herein.

Computer 30 may also communicate with: one or more external devices 39such as a keyboard, a pointing device, a display 40, etc.; one or moredevices that enable a user to interact with computer 30; and/or anydevices (e.g., network card, modem, etc.) that enable computer 30 tocommunicate with one or more other computing devices. Such communicationcan occur via Input/Output (I/O) interfaces 41. Also, computer 30 cancommunicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 42. As depicted, network adapter 42communicates with the other components of computer 30 via bus 33. Itshould be understood that although not shown, other hardware and/orsoftware components could be used in conjunction with computer 30.Examples include, but are not limited to: microcode, device drivers,redundant processing units, external disk drive arrays, RAID systems,tape drives, and data archival storage systems, etc.

Operation of authentication system 10 will be described below inrelation to preferred embodiments in which the product 23 is a medicaltest device and the digital signature σ is generated via a fuzzy-messagedigital signature scheme (FM-DSIG). An FM-DSIG scheme has a verificationalgorithm for verifying the digital signature σ in relation to fuzzydata, denoted by m′, within a predetermined difference measure of themessage data m as explained further below. FIG. 4 shows an exemplaryembodiment of a medical test device 45 and packaging 46 thereof. Testdevice 45 is a diagnostic test of a type, in common use in thehealth-care industry, which is operable by application of a fluid (e.g.blood or urine) to the test device. Such diagnostic tests are commonlyused to test for a wide variety of medical conditions. In the exampleshown, the test device 45 has diluent wells 47 to which the test fluidis applied in use. The diluent wells contain one or more chemicals whichdissolve in the test fluid and are conveyed by the fluid (e.g. via anabsorbent material or microchannels embedded in the test device) towardsa display window 48 of the device. One or more further chemicals may becontained within display window 48 to provide a chemical reaction if thetest result is positive, resulting in a visual indication of the testresult in the display window. The test device 45 also includes a messagedisplay window 49 for displaying a product message 50 comprising messagedata m₁. In this embodiment, the product message 50 is provided on thetest in a form which is (at least partially) hidden until the test isused. In particular, the test fluid is conveyed to message displaywindow 49 and reacts with one or more chemicals in the test window toreveal (or fully reveal) the product message 50. Examples of mechanismsfor implementing product message 50 are described further below. Testdevice 45 may also carry additional printed information, e.g. indicatingtest type and manufacturer details, as illustrated.

The packaging 46 carries the pack message 51, comprising message datam₂, and signature message 52 comprising the digital signature σ. In thisexample, the message data m₂ is represented in the form of text in packmessage 51, giving validity information such as test type, manufacturer,expiry date, etc., and also a URL (uniform resource locator) forsignature management server 12. The digital signature σ is representedin the form of a QR code providing signature message 52 in thisembodiment.

FIG. 5 illustrates an exemplary mechanism for representing the messagedata m₁ in product message 50 of test device 45. This shows amicrochannel 55 opening into message display window 49 in which apattern of chemical dots is printed. The chemicals react with the testfluid to reveal a dot pattern representing message m₁. The patterncorresponding to message m₁ may be revealed in various ways, e.g. viaone or a combination of dots becoming visible or invisible, or changingshape, size, color, etc. FIG. 6 shows another example in which themessage m₁ is encoded as a dot pattern 56 on a nitrocellulose membrane57. Again, the dot pattern may be revealed in various ways via reactionwith the test fluid and may use color coding and/or dotsappearing/disappearing, etc.

In operation of authentication system 10 for test device 45, verifiercomputer 11 is operated by a user who may be the patient or other party,such as a health care professional, overseeing use of the test. In thisapplication scenario, the verifier computer 11 is convenientlyimplemented by a mobile phone running an application which provides thefunctionality of verifier logic 19. The reader device 22 convenientlycomprises a camera integrated with the phone. After using the test, theuser uses reader device 21 to read the product message 50, the packmessage 51 and the signature QR code 52, here by capturing images of themessages using the camera. Verifier logic 19 includes appropriatefunctionality for interpreting the various images to extract the messagedata and digital signature presented in the messages. The verifiercomputer 11 thus reads, via reader device 22, the digital signature σ onthe packaging 46, and the message data m, comprising message m₁ on theproduct 45 and message m₂ on packaging 46. The verification logic 19then uses the verification key pk stored in memory 20 to verify thedigital signature σ in relation to the read message data obtained usingthe reader device 21. This verification procedure is performed using averification algorithm of the FM-DSIG scheme which provides forverification of the signature σ in relation to fuzzy data m′ within apredetermined difference measure of the message data m. In particular,inaccuracies inherent in mechanisms described above for representing theproduct message 50 may result in some degree of error in reading of thefirst message m₁. The resulting read message data, denoted by m₁′,corresponding to m₁ is treated as fuzzy data in which a limited degreeof error is permitted in the verification process. The second message m₂is treated here as a rigid message for which no error (fuzziness) ispermitted. The verification procedure will be described below for twoimplementations of the FM-DSIG scheme.

In the first FM-DSIG scheme, the digital signature σ generated in step 2of FIG. 1 comprises the first message m₁, the second message m₂, andsignature data Σ. In particular, the signature σ=(m₁∥m₂,Σ) where ∥denotes concatenation. The signature data Σ is generated in this step bysigning signature-input data, comprising the first message m₁ and thesecond message m₂, using the signing key sk. (The signature-input datahere may in general comprise m₁ and m₂ per se or some function thereofas illustrated further below). Steps of the verification procedure insystem 10 for the first FM-DSIG scheme are indicated in FIG. 7.

In step 60, verifier computer 11 reads the product message 50 to obtainthe read message m₁′ corresponding to the first message m₁ as describedabove. In step 61, verifier computer reads the signature QR code 52 toobtain the signature σ=(m₁∥m₂,Σ), and reads the pack message 51 toobtain read message data, denoted by m₂′, corresponding to the secondmessage m₂. In step 62, verifier logic 19 verifies the signature data Σin relation to the first message m₁ and second message m₂ as provided inm₁∥m₂ of the signature σ. This verification can be performed, using theverification key pk, via a verification algorithm of a standardsignature scheme as detailed below. In step 63, verifier logic 19determines if the read message data m′=m₂′ is within a predetermineddifference measure, denoted here by D, of the message data=m₁, m₂provided in the signature σ. As in this example only m₁′ is permitted tobe fuzzy, step 63 is performed by checking that m₂′=m₂, and that adifference (denoted here by Diff(m₁′, m₁)) between m₁′ and m₁ is nogreater than the difference measure D. The difference function Diff anddifference measure D may be defined here in various ways discussedbelow. Steps 62 and 63 constitute the verification algorithm of theFM-DSIG scheme here. In decision step 64, verifier logic 19 decideswhether the FM-DSIG verification is successful for the signature σ. Onlyif the signature data Σ is verified in step 62, and the read messagedata m′ is within the predetermined difference measure D of m in step63, is the signature determined to be valid (decision “yes” (Y) atdecision block 64). If either step 62 or step 63 fails (decision “no”(N) at decision block 64), then verifier logic 19 deems the signatureinvalid at step 65. An appropriate message can be displayed to the uservia user OF 21, and the verification operation terminates.

If the FM-DSIG verification succeeds at step 64, operation proceeds tostep 66 in which verifier logic 19 sends the read message data m′ andsignature σ to the signature management server 12 over network 13 viacommunications interface 18. Verifier logic may use the manufacturer URLprovided in pack message m₂ to access server 12, or the server addressmay be pre-stored in memory 20 in some embodiments. The signaturemanagement logic 15 of server 12 receives the read message data m′ andsignature σ via communications interface 14. In response, the signaturemanagement logic first checks in step 67 whether the received signaturehas been previously received and stored in signature set {σ} in database17. If so (Y at decision block 68), logic 15 sends a first notification,indicating that the signature is invalid, back to verifier computer 11in step 69. In response to receipt of the first notification, verifierlogic 19 deems the signature invalid at step 65 and operation terminatesas before. If the signature is not already stored in database 17 (N atdecision block 68), operation proceeds to step 70 in which logic 15performs the FM-DSIG verification process for the received (m′, σ),repeating the process performed in steps 62 and 63 by verifier logic 19.If the signature is found to be invalid, (N at decision block 71), thenoperation reverts to step 69, in which the first notification is sent toverifier computer 11, and continues as before. If the signature is foundvalid (Y at decision block 71), logic 15 sends a second notification,indicating that the signature is valid, back to verifier computer 11 instep 72. In response to receipt of the second notification, verifierlogic 19 deems the signature to be valid at step 73. Verifier computer11 can then display an appropriate message to the user via user I/F 21,and the verification process is complete.

The above process provides secure authentication of medical test device45, while the FM-DSIG verification process accommodates a limited degreeof error in the read product message m₁′ such as may arise due to thesmall space available for the product message and/or inaccuraciesinherent the message presentation mechanism. Since test device 45 isuniquely and authentically bound to its packaging 46, a fraudster cannotplace a genuine test device in different packaging, e.g. of another typeof test. The pack message m₂ can be read by a user to check validityinformation, and since this message is a rigid message for the purposesof verification, the read message m₂′ must be correct for signatureverification. Hence, a fraudster cannot modify the pack message, e.g. tochange expiry dates, without this being detected, or place an expiredtest in packaging with a valid expiration date. Product details, such asexpiration dates, manufacturer, test type, etc., can be verified withstrong guarantees, and users can rely on test results. A forger cannotcreate a new packaged product, or new packaging for a genuine product,having a valid signature, since this requires knowledge of the secretkey sk. Moreover, a valid signature can only be registered at signaturemanagement server once, preventing replication of messages and validsignatures from genuine products on counterfeits. The additional FM-DSIGverification check (step 70) at server 12, coupled with the fact thatthe product message is hidden on genuine test devices until use,inhibits abusive reporting of signatures from genuine products to server12 in an attempt to undermine the system.

Operation of system 10 for a second FM-DSIG scheme is indicated in FIG.8. With this scheme, the digital signature σ generated in step 2 of FIG.1 includes signature data Σ generated by encoding the first message m₁to produce an encoded message e(m₁) which comprises the first message m₁and parity data p, and signing signature-input data, comprising thefirst message m₁ and the second message m₂, using the signing key sk.(The signature-input data here may in general comprise m₁ and m₂ per se,or may comprise the encoded message e(m₁) and m₂, or may comprise somefunction of these elements as illustrated below). The digital signatureσ includes the parity data p in this scheme, i.e. α=(p,Σ). Steps 80 and81 of FIG. 8 correspond to steps 60 and 61 of FIG. 7 in which verifiercomputer 11 reads the product message 50 to obtain the read message datam₁′, the signature QR code 52 to obtain the signature σ=(p,Σ), and thepack message 51 to obtain the read message data m₂′. In step 82,verifier logic 19 then decodes the read message data m₁′ using theparity data p in the signature to obtain a decoded message, denoted bym₁*. That is, the verifier logic decodes m₁′∥p to obtain the decodedmessage m₁*. In step 83, verifier logic 19 then verifies the signaturedata Σ in relation to the decoded message m₁* and the read secondmessage m₂′. This verification can be performed, using the verificationkey pk, via a verification algorithm of a standard signature scheme asdescribed below. Note that decoding step 82 will give a decoded messagem₁* equal to the first message m₁ if the read message data is within apredetermined difference measure of the first message m₁. Thisdifference measure is determined by the error-correcting limit of theencoding scheme used to encode the first message m₁ and generate theparity data p. If this difference measure is exceeded (m₁′ is toodifferent from m₁ and therefore contains too many errors) the decodedmessage m₁* will not equal m₁ and signature verification step 83 willfail. As before, successful signature verification requires that m₂′=m₂.

Steps 82 and 83 thus constitute the verification algorithm of the secondFM-DSIG scheme. Subsequent steps 84 through 93 correspond respectivelyto steps 64 through 73 of FIG. 7. This second scheme provides alladvantages of the first scheme above, with the additional advantage thatmessage data is hidden in the digital signature σ, i.e. the signature σdoes not reveal the message data per se but only the parity data p.

The procedures of FIGS. 7 and 8 can be readily adapted for scenarios inwhich use of a second, rigid message m₂ is not required simply byomitting features specific to m₂ from the operations described.

Exemplary constructions for the FM-DSIG schemes of FIGS. 7 and 8 aredescribed in detail below. Some preliminaries are described first.

Basic Functions

Definition 1 (Bilinear Maps)

Let

₁,

₂, and

_(T) be groups of prime order q. A map e:

₁×

₂→

_(T) is called a bilinear map if it satisfies:

bilinearity: ∀u₁∈

₁, ∀u₂∈

₂, ∀x, y∈

, e(u₁ ^(x),u₂ ^(y))=e(u₁,u₂)^(xy);

non-degeneracy: for all generators g₁∈

₁ and g₂∈

₂, e(g₁,g₂) generates

_(T); and

efficiency: there exists an efficient algorithm

(1^(λ)) that outputs the bilinear group (q,

₁,

₂,

_(T), e, g₁, g₂) and an efficient algorithm to compute e(u₁,u₂) for anyu₁∈

₁, u₂ ∈

₂. If

₁=

₂ the map is symmetric and otherwise it is asymmetric.

Definition 2 (Binary Hamming Distance).

The binary Hamming distance d₂(M, N) between two binary matrices of samedimensions M, N is the number of bits where those matrices differ.

Block Codes

Definition 3 (Binary Block Codes).

A binary block code is an injective mapping C: 2^(k)→2^(n) where k isthe message length and n is the block length. A message is any elementin 2^(k), while the code C is the set of all images.

In the above definition it is worth noting that although codewords arestrings of length n, not all elements in 2^(n) are codewords. A stringof n bits is only considered a codeword if it is the image of a k-bitstring.

Binary block codes are denoted by [n, k, d_(min)]₂, where d_(min) is theminimum distance of the code, as described in Definition 5. A binarycode can also be denoted by a simplified notation where the minimumdistance is omitted, i.e., [n, k]₂. The number n k is the redundancy ofthe code.

Definition 4 (Rate of a Code).

The rate of a block code is defined as the ratio between its messagelength and its block length, that is R=k/n.

Definition 5 (Minimum Distance).

The minimum distance d_(min) of a block code is the minimum number ofpositions in which any two distinct codewords differ.

Theorem 1 (Error Detection Capabilities).

A binary code C can detect up to k errors in any codeword if and only ifd_(min)≥k+1.

Theorem 2 (Error Correction Capabilities).

A binary code C can correct up to k errors in any codeword if and onlyif d_(min)≥2k+1.

Definition 6 (Binary Error-Correcting Codes). A binary error-correctingcode (binary ECC) is a [n, k, d_(min)]₂ code that has both an encodingfunction e: {0,1}^(k)→{0,1}¹¹, and a decoding function d{0,1}^(n)→{0,1}^(k). The encoding function maps messages to codewords,while the decoding function takes any string in the range {0,1}^(n) andmaps it back to a message.

Note that decoding functions in binary ECC codes can map differentelements of 2^(n) into the same message, and thus are not injectivemappings.

Definition 7 (Linear Block Codes).

A binary linear block code [n, k]₂ is a k-dimensional subspace of then-dimensional vector space.

Definition 8 (Generator Matrix).

A generator matrix G of a binary linear block code [n, k]₂ is a k×nmatrix whose rows form a basis for the k-dimensional subspace of then-dimensional vector space. G can be rearranged in a standard formG=[I_(k)|P], where I_(k) denotes the k×k identity matrix, and P is somek×(n−k) matrix, called the parity matrix.

The above definition implies that the codewords of a code C are obtainedvia v=xG, and therefore have the form x₁, . . . , x_(k), p₁, . . .p_(n-k), . . . where x=x₁, . . . , x_(k) is the original message, andp₁, . . . p_(n-k) are parity bits.

Definition 9 (Parity Check Matrix).

Given a linear code C with generator matrix G, an (n−k)×n matrix H iscalled a parity check matrix for C if and only if for every codewordv∈C, HV^(T)=0 (with v^(T) being the transpose of vector v). This meansthat to every G=(I_(k)|P), a parity check matrix H=(−P^(T)|I_(n-k)) canbe associated.

Syndrome Decoding.

Let C=[n, k, d_(min)] be a linear code with generator G and parity checkmatrix H. From Theorem 2, C can correct up to t=└(d_(min)−1)/2┘ errors.Assume that to an encoded message v=xG, up to t errors are added. Themessage then becomes u=xG+e, where e is a binary string that has 1 ineach position where the errors occurred. When we calculate Hu^(T), weobtain:Hu ^(T) =H(v ^(T) +e ^(T))=0+He ^(T) =He ^(T)

To decode, a syndrome dictionary needs to be stored. This dictionarycontains all possible t-error vectors along with their syndromesHe^(T)=s. When decoding, first calculate the syndrome s=He^(T), look ups in the dictionary to find e, and compute v=u+e.

Hamming Codes.

A Hamming code is a code in which a parity check matrix H, withdimensions (n−k)×n, is formed by all possible non-zero binary vectors(n−k)×1 in any order, so that the last n−k columns form the identitymatrix I_(n-k). For example, the Hamming Code C=[7, 4, 3]₂ has paritycheck matrix

$H = \begin{bmatrix}0111100 \\1011010 \\1101001\end{bmatrix}$

Messages are vectors x=x₁, x₂, x₃,x₄, and codewords are vectors v=x₁,x₂, x₃,x₄, p₁, p₂, p₃. Since d_(min)=3, the code C can correct up tot=└(3−1)/2′=1 error.

Digital Signatures

Definition 10 (Digital Signatures).

A digital signature scheme is a triple of polynomial-time algorithmsDSIG=(gen, sig, ver) together with a message space

where:

gen(λ): takes as input a security parameter and outputs a key pair(pk,sk).

sig(sk,m): takes as input a signing key sk and a message m∈

, and outputs a signature σ.

ver(pk,m′,σ): takes as input a verification key pk, a message m′ and apurported signature σ, and outputs valid or invalid.

Correctness.

A digital signature scheme is said to be correct if for all

and all messages m∈

, it holds that valid←ver(pk,m,sig(sk,m)).

The standard security notion for signature schemes is called existentialunforgeability under an adaptive chosen message attack. For ourpurposes, we need a slightly different notion. A security notionsatisfying our requirements is called existential unforgeability under aweak chosen message attack (eu-w-cma) as discussed further below.

The Boneh Boyen Short Signature Scheme.

Let

₁,

₂ and

_(T) be groups of prime order q with log_(q)>λ that allow for a bilinearmap:

₁×

₂→

_(T). The components of Boneh Boyen's short signature scheme (describedin “Short signatures without random oracles and the SDH assumption inbilinear groups”, Boneh & Boyen, J. Cryptology, 21(2):149-177, 2008) areas follows:

gen(λ): select random generators g₁∈

₁ and g₂∈

₂, and a random integer x→Z_(q)*. Compute v←g₂ ^(x) and c←e(g₁, g₂)∈

_(T). Output pk=(g₁, g₂, V, c) and sk=(g₁, x).

sig(sk,m): on input m∈Z_(q), parse sk as (g₁,x) and output σ=g₁^(1/(x+m)) ∈

₁. In the unlikely event that x+m=0 (mod p), sig(sk,m) outputs σ=1 ∈

₁.

ver(pk,m′,σ): parse pk as (g₁,g₂,v,c). If e(σ,v·g₂ ^(m))=c or if σ=1 andv·g₂ ^(m)=1, output valid. Otherwise output invalid.

Observe that c is pre-computed and included in the public key to addefficiency to the verification algorithm. In this case, g₁ can beomitted from the public key. We will consider the case where

₁≠

₂ since the elements of

₁ may have a shorter representation than those of

₂, and thus we can obtain the shortest possible signatures.

Theorem 3 (Security of Boneh Boyen's Short Signature Scheme).

The above construction is existentially unforgeable against weak chosenmessage attacks under the q-SDH assumption.

Fuzzy-Message Digital Signatures (FM-DSIG)

We define the notion of fuzzy-message digital signature (FM-DSIG)schemes, where a signature can verify a message as authentic even ifpart of the message has been slightly corrupted, i.e., it allows part ofthe message to be fuzzy. In order to restrain adversaries from producingvalid forgeries however, only a certain degree of corruption is allowed.

Definition 11 (Fuzzy-Message Digital Signatures)

A fuzzy-message digital signature scheme is a tuple of polynomial-timealgorithms FM-DSIG=(fgen, fsig, fver, fclo) together with a messagespace

=

₁×

₂, where

₁ is the space of fuzzy messages and

₂ is the space of rigid messages, i.e., messages that cannot be altered.The tuple of algorithms work as follows.

fgen(λ): takes as input a security parameter and outputs a key pair(pk,sk).

fsig(sk,m): takes as input a signing key sk and a message m=m₁∥m₂ ∈

₁×

₂, and outputs a signature σ.

fver(pk,m′,σ): takes as input a verification key pk, a messagem′=m₁′∥m₂′ and a purported signature σ, and outputs valid or invalid.

fclo(m,m′): takes as input two messages m=m₁∥m₂ ∈

₁×

₂ and m′=m₁′∥m₂′ ∈

₁×

₂ and outputs 1 if m₁ and m₁′ are close to each other and m₂=m₂′.

Correctness.

A fuzzy-message digital signature scheme is said to be correct if forall

and all messages=m₁∥m₂, m′=m₁′∥m₂′∈(

₁×

₂)² with fclo(m,m′)=1, it holds that valid←fver(pk,m′,fsig(sk,m)).

Fuzzy Existential Unforgeability Under Weak Chosen Message Attacks(Feu-w-Cma).

This notion is an adaptation of the eu-w-cma notion for signatureschemes mentioned above to the fuzzy-message signature scenario. Letf(m) be the set of all messages m* with fclo(m, m*)=1 and let (f(m),σ)represent all pairs consisting of one element of f(m) and the signatureσ. A fuzzy-message digital signature scheme with message space

=

₁×

₂ is said to be existentially unforgeable against weakly chosen messageattacks if no adversary

can win the following experiment with non-negligible probability in thesecurity parameter λ.

Query.

Receive from

a list of messages m¹, . . . , m^(q), where each message m^(i), i=1, . .. , q, can be written as m₁ ^(i)∥m₂ ^(i)∈

₁×

₂, and add them to a list Q.

Response.

Run

and generate σ^(i)←fsig(sk,m^(i)) for i=1, . . . , q. Hand pk and the qsignatures σ¹, . . . , σ^(q) to

.

Output.

Eventually

outputs (m*,σ*) with m*:=m₁*∥m₂*, and wins the experiment if all of thefollowing conditions hold.

1. m*∈

₁×

₂,

2. (m*, σ*) is not any of (f(m¹),σ¹) . . . , (f(m^(q)), σ^(q)), and

3. fver(pk,m*,σ*)=valid.

First FM-DSIG Construction

Let DSIG=(gen, sig, ver) be an ordinary (i.e., non-fuzzy) digitalsignature scheme where messages are distributed over a message space

₂. Let ƒ:

₁×

¹→{0, 1} be a similarity function, and let H:

₁→

₂ be an invertible mapping that maps elements of

₁ into elements of

₂. We construct a basic fuzzy-message digital signatureFM-DSIG_(basic)=(fgen, fsig, fver, fclo), over message space

=

₁×

₂, as follows.

fgen(λ): identical to gen(λ).

fsig(sk,m): on input m=m₁∥m₂ ∈

₁×

₂, output σ←(m,sig(sk,H(m₁)+m₂)). The signature-input data describedabove is thus H(m₁)+m₂ here.

fver(pk,m′,σ): parse the signature σ as σ←(m,Σ), with m=m₁|m₂ ∈

₁×

₂. Output valid if ver(pk,H(m₁)+m₂,Σ)=valid and fclo(m,m′)=1. Otherwiseoutput invalid.

fclo(m,m′): on input two messages m=m₁∥m₂∈

₁×

₂ and m′=m₁′×m₂′∈

₁×

₂, the closeness function outputs 1 if ƒ(m₁, m₁′)=1 and m₂=m₂′.

Instantiation.

We use the Boneh Boyen short signature scheme described above as theordinary digital signature scheme, and the binary Hamming distance,described in Definition 2, to build the similarity function ƒ. Let

₁,

₂ and

_(T) be groups of prime order q with log_(q)>λ that allow for a bilinearmap

₁×

₂→

_(T). Also, let ƒ: {0,1}^(k)×{0,1}^(k)→{0, 1} be a function that takestwo bit-strings of length k and outputs 1 if the Hamming distancebetween those strings is not greater than a bound r. Note that bydefinition r cannot be greater than the length of the messages. Thecomponents of our FM-DSIG_(basic) scheme over message space {0,1}^(k)×

_(q) work as follows.

fgen(λ): select random generators g₁∈

₁ and g₂ ∈

₂, and a random integer x←Z_(q)*. Compute v←g₂ ^(x) and c←e(g₁,g₂)∈

_(T). Output pk=(g₁,g₂,v,c) and sk=(g₁,x).

fsig(sk,m): on input m=m₁∥m₂∈{0,1}^(k)×

_(q), parse sk as (g₁,x) and output σ←(m, g₁ ^(1/(x+H(m) ¹ ^()+m) ² ⁾).In the unlikely event that x+H(m₁)+m₂=0 (mod q), fsig(sk,m) outputsσ=(m,1).

fver(pk,m′,σ): parse pk as (g₁,g₂,v,c) and σ as σ←(m₁∥m₂,Σ). Check ifone of the following conditions hold:

1. e(Σ,v·g₂ ^(H(m) ¹ ^()+m) ² )=C or

2. Σ=1 and v·g₂ ^(H(m) ¹ ^()+m) ² =1.

If so and if fclo(m, m′)=1, output valid. Otherwise output invalid.

fclo(m, m′): on input two messages m=m₁∥m₂∈{0,1}^(k)×

_(q) and m′=m₁′∥m₂′∈{0,1}^(k)×

_(q) output 1 if and only if ƒ(m₁, m₁′)=1 and m₂=m₂′.

Although in the above instantiation we are assuming that messagesm=m₁∥m₂ are elements in {0,1}^(k)×

_(q), we could instead sign any message m∈{0,1}*∈{0,1}* by appropriatelyapplying collision-resistant hash functions to the messages.

Second FM-DSIG Construction Based on Error-Correcting Codes

Let DSIG=(gen, sig, ver) be an ordinary (non-fuzzy) digital signaturescheme where messages are distributed over a message space

₂. Let C be an [n,k,d_(min)]₂ code with encoding function e:{0,1}^(k)→{0,1}^(n), and a decoding function d: {0,1}^(n)→{0,1}^(k), andlet H: {0,1}^(n)→

₂ be an invertible mapping that maps elements of {0,1}^(n) into elementsof

₂. We construct a fuzzy-message digital signature FM-DSIG_(ecc)=(fgen,fsig, fver, fclo) over message space

={0,1}^(k)×

₂ which hides the fuzzy message, i.e. the fuzzy message is not revealedin the signature, as follows.

fgen(λ): identical to gen(λ).

fsig(sk,m): on input m=m₁∥m₂∈{0,1}^(k)×

₂, encode m₁ as e(m₁):=m₁∥p where p=parity bits. Output σ←(p,sig(sk,H(e(m₁))+m₂)). The signature-input data described above is thusH(e(m₁))+m₂ here.

fver(pk,m′,σ): on input m′=m₁∥m₂, parse σ as σ←(p,Σ), and decode m₁∥p asm₁*←d(m₁′∥p). Output valid if ver(pk,H(m₁*∥p)+m₂′,Σ)=valid. Otherwiseoutput invalid.

fclo (m,m′): The closeness function on input two messagesm=m₁∥m₂Σ{0,1}^(k)×

₂ and m′=m₁*∥m₂′∈{0,1}^(k)×

, outputs 1 if the number of 1's in m₁γm₁′ is at most └(d_(min)−1)/2┘,the error-correcting capability of the code, and m₂=m₂′.

Note that in the above construction, if m₁=m₁′ differ in at most└(d_(min)−1)/2┘, bits then, by the error-correction capability of C,m₁*←d(m₁′∥p) will equal m₁. Therefore, as long as m₂=m₂′, theverification algorithm will output valid.

Instantiation.

We use the Boneh Boyen short signature scheme described above as theordinary digital signature scheme, and let C be a Hamming Code[n,k,d_(min)]₂ as described above. Let

₁,

₂ and

_(T) be groups of prime order q with log_(q)>λ that allow for a bilinearmap:

₁×

₂→

_(T). Let G and H be the generator and parity check matrices,respectively, of the error-correcting code C, and let H: {0,1}^(n)→

_(q) be an invertible function. The algorithms of FM-DSIG_(ecc) whichaccepts messages in {0,1}^(k)×

_(q) are as follows.

fgen(λ): select random generators g₁∈

₁ and g₂∈

₂, and a random integer x←Z_(q)*. Compute v←g₂ ^(x) and c←e(g₁,g₂)∈

_(T). Output pk=(g₁,g₂,v,c) and sk=(g₁,x).

fsig(sk,m): on input m=m₁∥m₂∈{0,1}^(k)×

_(q), encode m₁ as e(m₁):=m₁·G=m₁|p. Parse sk as (g₁,x) and compute g₁^(1/(x+H(e(m) ¹ ^())+m) ² ⁾←sig(sk,H(e(m₁))+m₂). In the unlikely eventthat x+H(e(m₁))+m₂=0 (mod q), sig(sk, H(e(m₁))+m₂) outputs 1. Outputσ←(p,g₁ ^(1/(x+H(e(m) ¹ ^())+m) ² ⁾).fver(pk,m′,σ): on input m′=m₁′∥m₂′, parse pk as (g₁,g₂,v,c) and a as(p,Σ). Compute the syndrome s←H·(m₁′|p)^(T). Search for (s,e) in asyndrome dictionary, where e is an error bit string associated to thesyndrome s. Compute m₁*=(m₁′|p)+e. Check if one of the followingconditions hold:1. e(Σ,v·g₂ ^(H(e(m) ^(i) ^(*))+m) ² ^(′))=c or2. Σ=1 and v·g₂ ^(H(e(m) ^(i) ^(*))+m) ² ^(′))=1.If so, output valid. Otherwise output invalid.fclo(m,m′): The closeness function on input two messages m=m₁∥m₂∈{0,1}^(k)×

_(q) and m′=m₁′∥m₂′∈{0,1}^(k)×

_(q), outputs 1 if the number of 1's in m₁⊕m₁′ is at most└(d_(min)−1)/2┘, the error-correcting capability of the code, andm₂=m₂′.

Using the above FM-DSIG constructions in the medical test deviceapplication, the product manufacturer can obtain a verification/signingkey pair via

and then register the verification key pk with a certificate authorityCA. Users who wish to verify the authenticity of products will use averification computer 11 containing the algorithms fver, fclo ofFM-DSIG, and the verification keys of all trusted CAs. The manufacturergenerates the digital signature σ=fsig(sk,m₁∥m₂). After using the test,the verifier computer can select the verification key pk correspondingto product manufacturer, and run fver(pk,m′,σ) to determine whether σ isa valid signature for the read messages m₁′, m₂′ in m′. If σ is valid,the verifier computer accesses signature management server 12, using theURL contained in m₂, to report (m′,σ) as described above. Server 12 alsoruns fver(pk,m′,σ) to check signature validity as described. Using thesecond construction above, the FM-DSIG scheme is feu-w-cma secure,protecting against forgeries even on previously signed messages (andalso messages close to those).

Many changes and modifications can of course be made to the exemplaryembodiments described. For example, the fuzzy message could be visiblebefore the test is used. This would allow clinics, doctors, etc., toverify the authenticity of the product without having to use it. Whereverification may be performed for products of multiple differentmanufacturers, the number of trusted verification keys stored byverification computers could be reduced by having the signature σ signedby a chain of certificate authorities. Verification computers would thenonly need to store verification keys of root CAs.

The schemes described can be applied to other forms of medical testdevice, e.g. nitrocellulose based test strips, and to any other productsfor which authentication may be required. It will be apparent that theembodiments described are especially advantageous where there is limitedspace for the message to be authenticated and the space limitation meansthat a message may be inaccurately printed or read and constrains addedredundancy for the fuzzy message. Messages may of course be applied toproducts/packaging in other ways, e.g. using tamper-proof stickers, ormay be otherwise printed on or embedded in products/packaging in anyconvenient manner. Also, scenarios can be envisaged in whichverification of signatures by verifier computer 11 is sufficient forauthentication, i.e. signature management server 12 is not required.Steps performed by server 12 might be performed by verifier computer 11in some scenarios.

The difference measure D for the FM-DSIG scheme may be implemented invarious other ways as will be apparent to those skilled in the art. Forinstance, a difference measure based on Euclidean distance may be usedin other embodiments. The second FM-DSIG scheme above may of course bebased on codes other than binary codes.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for producing an authenticated packagedproduct, the method comprising: generating, by a manufacturer computer,a digital signature, dependent on message data for the product, via afuzzy-message digital signature scheme using a secret signing key;printing, by a product manufacturer, the message data as a pattern ofchemical dots on the product; printing, by the product manufacturer, thedigital signature as ink-printed dots on the packaging; and packing, bythe product manufacturer, the product in the packaging.
 2. The method asclaimed in claim 1, further comprising: verifying, by a verificationlogic, that the digital signature is within a predetermined differencemeasure of said message data, according to a verification algorithm ofthe fuzzy-message digital signature scheme.
 3. The method as claimed inclaim 2, further comprising: printing, by the product manufacturer, themessage data as a first message m1 on the product; generating, by themanufacturer computer, signature data Σ by signing signature-input data,comprising the first message m1, using the secret signing key; andprinting, by the product manufacturer, the digital signature as thefirst message m1 and the signature data Σ.
 4. The method as claimed inclaim 2, further comprising: printing, by the product manufacturer, themessage data as a first message m1 on the product; generating, by themanufacturer computer, a second message m2; generating, by themanufacturer computer, signature data Σ by signing signature-input data,which comprises the first message m1 and the second message m2, usingthe secret signing key; and printing, by the product manufacturer, thedigital signature as the first message m1, the second message m2, andthe signature data Σ on the packaging where the message data is notprinted.
 5. The method as claimed in claim 4, further comprisinggenerating, by the manufacturer computer, the signature-input data asH(m1)+m2 where H is an invertible function which maps m1 to a signaturespace for the fuzzy-message digital signature scheme.
 6. The method asclaimed in claim 2, further comprising: generating, by the manufacturercomputer, the message data comprising a first message m1; printing, bythe product manufacturer, the message data on the product; generating,by the manufacturer computer, signature data Σ by encoding the firstmessage m1 to produce an encoded message e(m1) which comprises the firstmessage m1 and parity data p, and signing signature-input data, whichcomprises the first message m1, using the secret signing key; andprinting, by the product manufacturer, the digital signature as thefirst message m1, the parity data p, and the signature data Σ on thepackaging where the message data is not printed.
 7. The method asclaimed in claim 6, wherein generating the signature data Σ includessigning the signature-input data comprising the first message m1 and theencoded message e(m1), using the secret signing key.
 8. The method asclaimed in claim 6, further comprising: printing, by the productmanufacturer, a second message m2 on the packaging where the digitalsignature is printed; and signing, by the manufacturer computer, thesignature-input data that comprises the first message m1 and the secondmessage m2, using the secret signing key.
 9. The method as claimed inclaim 8, further comprising generating, by the manufacturer computer,the signature-input data as H(e(m1))+m2 where H is an invertiblefunction which maps e(m1) to a signature space for the signature scheme.10. The method as claimed in claim 1, wherein: the product is a medicaltest device that is operable to alter the appearance of a printedindicator by application of a fluid to the device; and the message datais printed on the device as a concealed part of the printed indicator,the method further comprising: a product user revealing the message databy application of the fluid to the device.
 11. The method as claimed inclaim 10, further comprising: printing, by the product manufacturer, asecond message m2 on the packaging as part of the message data; andproducing, by the manufacturer computer, the digital signature fromsignature data Σ generated by encoding the first message m1 to producean encoded message e(m1) which comprises the first message m1 and paritydata p, and signing signature-input data, comprising the first messagem1 and the second message m2, using the secret signing key, wherein thedigital signature includes the parity data p.
 12. The method as claimedin claim 11 wherein the second message m2 is represented on thepackaging in the form of text giving validity information relating tothe device.